The group's early consensus is clear: reach a deal, agree to set spending figures for the upcoming fiscal year and replace unpopular, across-the-board spending cuts for one, maybe two, years.

From there it gets more complicated.

The lawmakers tasked with finding that agreement largely fell back behind old battle lines that have tripped up previous negotiations, particularly over revenue.

"I want to say this from the get-go: If we look at this conference as an argument about taxes, we're not going to get anywhere," Ryan warned.

However, Senate Majority Leader Harry Reid, D-Nev., offered a one-word answer when asked Tuesday whether he could accept a budget deal that didn't include new revenues: "No."

Senate Budget Committee Chairwoman Patty Murray, D-Wash., is equally unlikely to agree to any budget deal that replaces the unpopular cuts, known as the sequester, with other spending cuts alone. Murray was also candid about the prospects for reaching a deal.

"It won't be easy," she said, "It will require both sides to step out of their comfort zone and ideological corners, and we won't be able to tackle every one of our nation's challenges in these few short weeks."

Democrats are seeking additional revenues through closing tax loopholes and ending corporate tax breaks. "The tax loopholes I'd like to devote to deficit reductions are ones we should get rid of anyway. Big oil does not need taxpayer subsidies; companies should not be rewarded for shifting assets to foreign countries," said Sen. Sheldon Whitehouse, D-R.I.

Some Republicans, including Rep. Tom Cole, R-Okla., said they are open to such proposals as long as individual taxpayer rates are not affected and Democrats put some equally tough measures on the table, such as savings from entitlement programs like Medicare, and support for a comprehensive overhaul of the federal tax code.

The pace of negotiations is moving slowly despite a Dec. 13 deadline established in the recent short-term agreement to end the government shutdown and suspend the debt ceiling. The next meeting is not for two weeks. There are only 16 legislative days remaining on the House calendar.

Budget negotiators are tasked with coming up with a deal that can pass a divided Congress by Jan. 15, which is when the current stopgap funding bill runs out.

At the very least, said Sen. Lindsey Graham, R-S.C., another government shutdown should be off the table. "That would be good for all of us," he said, "We're not going to be able to reconcile our different visions between now and September but we should be able to fund the government."

If budget negotiators fail, Congress can approve another stopgap funding bill that keeps the government running on autopilot.

However, budget hawks received some positive news Wednesday as the government said the annual deficit fell to $680 billion, the lowest gap between the government's revenue and spending since 2008, the result of a growing economy and tax increases and spending cuts that took effect this year.